Electrical control system



1934- c. G. SUITS ELECTRICAL CONTROL SYSTEM Filed July 25, 1931 Inventor Chaunce GLSuitS, by M5.

Hi5 Attorney.

Patented Aug. 7, 1934 I v. 1,900,581 nnnc'rarou. oom'nor. srs'rm Chauncey 6.. Suite, Schenectady, N.- y., assignor to General Electric Company, a corporation of New York Application July :5, 19:1,seria1 No. 553,128

'lClaims.

My invention relates to electrical control systems and particularly to improvements in electrical control systems of the type including relatively delicate contacts which control the operation of a relatively large currentponsuming inductive translating device.

There are many instances where relatively delicate control contacts are used to controlthe operation of an electrical translating device through an intermediate relay, or relays, possessing a relatively highly inductive winding. The relatively delicate contacts are often the contacts of a contact-making meter, such for example as a contact-making wattmeter. Such meters are usul5 ally mounted on meter panels which are adjacent large operating machines and which consequently are subject to considerable vibration. The result is that the contacts are often brought into vibratory, or trembling, engagement with each .20 other with the result that damaging contact arcing takes place due to the relatively high inductance of the relay coil and consequently the life and operation of the contacts is adversely affected. Furthermore, most of the relays in such systems are lighter and smaller than desirable so as to possess as small an inductance as possible.

As a result their inertia characteristics are such as to cause chattering when they are energized from an ordinary commercial frequency alternating current circuit. In addition the vibration of the contacts often causes a momentarydisengagement thereof at a time when engagement, is desired or necessary.

I have found that the use of a saturable core reactor between the delicate vibratory contacts and the inductive load provides a very simple and inexpensive solution of all of the operating difllculties enumerated above. Thus, as a saturable core reactor is a power amplifier, the

\ 40 delicate contacts are required to handle only small currents, whilethe' relay, which is controlledby these contacts, may be made more rugged and heavy so that chattering, when it is operated by commercial frequency alternating current, is eliminated.

While my invention is not limited to the use of any particular type of saturable core reactor I Y prefer to use a reactor whose alternating current winding, or windings, creates a closed loop circuit.

A number of alternative structural examples of such a reactor are disclosed in Patent No. 1,331,875, granted on April 20, 1920, on an appli-' cation of E. F. W. Alexanderson. The reason that I prefer to employ such a reactor is that I have found that the closed loop made by the alternating current winding, or windings, of the reactor so retards the rate of change of flux in the core of the reactor that not only is contact sparking greatly reduced but also a desirable time characteristic is introduced into the system which minimizes the harmful operating effect of accidental momentary engagement of the control contacts.

I also prefer to control the energization of the direct current saturating winding of my reactor through a full wave rectifier, or from a half wave rectifier when the direct current winding has associated therewith an asymmetrical conducting device in the manner disclosed and claimed in a copending application, Serial No. 553,816, filed July 29, 1931, in the name of H. A. Droitcour and assigned to the assignee of the present application. The reason that I prefer to employ such control arrangements is that they aid the efiect of the alternating current windings of the reactor in reducing contact sparking and in the production of a desirable time characteristic for the reactor. The operation of these features will be described in detail in connection with the operation of my invention.

An object of my invention is to provide an inexpensive and simple arrangement for obtaining satisfactory control of an inductive translating device by the delicate contacts of a contact making device which may be subject to vibration.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring now to the single figure of the accompanying drawing, wherein I have shown diagrammatically an embodiment of my invention,. 1 is a contact making control device, shown as a polyphase contact making wattmeter, which is connected by means of potential transformers 2 and current transformers 3 to respond to the power flow in a three-phase alternating current circuit 4. Meter 1 is provided with a suitable set of control contacts which are illustrated as a movably mounted contact 5 and a pair of relatively stationary cooperating contacts 6 and 7. I have illustrated, byway of example, an application of my invention to a load regulating system and consequently contacts 5, -6, and '1 control through intermediate apparatus a small reversible servo or pilot motor 8 which operates a steam valve 9 V for controlling the flow of steam to a turbine 10 which is connected to operate an alternating current generator 11, which in turn is connected to feed its output into circuit 4.

The intermediate apparatus consists essentially of a pair oi saturable reactors 14 and 15 which determine the operation oi. a pair of relays, or contactors, 12 and 13, which in turn act as means for controlling the direction of rotation of motor 8. Reactors 14 and 15 are of the type illustrated in the above mentioned Alexanderson patent. Thus reactor 14 is provided with a pair of parallel connected alternating current windings 16 and 17 and a pair of direct current windings 18 and 19. As shown, windings 16 and 18 are wound on a separatecore irom windings 1'7 and 19. Alternating current windings 16 and 17 are connected in parallel with each other and in series with the operating coil of relay l2, and a resistance 20, across a suit able source of alternating current, such as a supply bus 21.

In accordance with the broader aspects 01' my invention it is immaterial whether the direct current windings of reactor 14 are energized from a direct current source of supply or through a rectifier from an alternating current source. However, I secure desirable operating features by energizing the direct current windings from an alternating current source through a full wave rectifier and consequently I connect windings 18 and 19 in series opposition through a full wave rectifier, illustrated as of the bridge connected contact type, 22, and through contacts 5 and 6 to the alternating current supply circuit 21. In a similar manner, alternating current windings 23 and 24 of reactor 15 are connected in parallel with each other and in series with a resistance 25 and operating coil of relay 13 across source 21. Also direct current windings 26 and 27 of reactor 15 are connected in series opposition through a rectifier 28, which is similar to rectifler 22, in series with contacts 5 and 7 across source 21.

It should be distinctly understood that reactors 14 and 15 are merely diagrammatically illustrated and that many other equivalent well known types of reactors may be employed, as for example a three-legged core reactor having parallel connected alternating current windings on its outer legs and a direct current saturating control winding on its inner leg, or a well known type of four-legged core reactor having a pair 0! parallel connected alternating current windings on its two inner legs and a direct current control winding linking both of the inner legs may also be employed without departing from my invention in its broader aspects. g

The purpose of connecting the direct current windings of the reactors in series opposition is that the instantaneous alternating current voltages in the windings will then mutually neutralize each other.

The operation of the arrangement illustrated in the drawing is as follows. Assume that turbine 10 is operating generator 11 and that the power flow in circuit 4 has just exceeded a predetermined normal value, thereby causing the engagement of contacts 5 and 6 of meter-l. In this case the contacts will complete an energizing circuit for the direct current windings of reactor 14 through rectifier 22 with the result that the cores of this reactor become magnetically saturated thereby decreasing the impedance of the alternating current windings. This causes an increase in current to flow through the operating coil of relay 12, thereby causing this relay to close with the result that an operating circuit for motor 8 is completed.-This circuit is such as to cause this motor to operate valve 9 to decrease the steam supply to turbine 10 thereby decreasing the power output of generator 11. This action will continue until the power flow in circuit 4 is normal when contact 5 will disengage contact 6. In a similar manner if the power flow falls below normal, contact 5 engages contact 7 thereby causing saturation of reactor 15, the operation of relay l3 and the reversal of motor 8, whereby valve 9 admits more steam to turbine 10 thereby increasing the power output of the generator 11.

The way in which the reactors l4 and 15 serve to substantially eliminate contact sparking and also to introduce a desirable time characteristic into the operation of the system is as follows: The rapidity with which the flux in the cores of reactor 14, for example, changes determines both the rate of change of impedance of windings 16 and 17 to the alternating current and also the degree to which sparking at the contacts 5 and 6 can occur.

Thus consider the situation when the flux in the cores oi reactor 14 has attained a certain maximum value due to the presence of the direct current furnished by rectifier 22. When the circuit is broken by contacts 5 and 6 the usually almost instantaneous change of flux which normally causes sparking is prevented by the presence of two closed circuits one of which comprises alternatlng current windings l6 and 17 and resistance 20 and the other of which comprises direct current windings l8 and 1,9 and rectifier 22, which acts as a low resistance path for the build down current in the direct current windings. The subsequent rate of change of flux is determined by the ratio of inductance to resistance of these two coupled circuits, this ratio being known as the time constant of an inductive circuit.

This ratio is, in practical cases, greater for the former circuit which therefore predominately determines the rate of change of ilux. This may be seen to be necessarily the case, since, in general, the ratio of inductance to resistance for the windings 16 and 1'7 is identical; but the direct current saturating circuit has included therein the series resistance comprising the rectifier 22 which is effective in reducing the time constant of this series circuit. The time constant of a circuit of this type, defined in the ordinary manner, may be of the order of seconds, so that substantially no arcing in the contacts 5 and 6 occurs when the alternating current impedance of the windings 16 and 17 changes at a corresponding low rate. Time delay characteristics are thus at tained and the magnitude of the time delay is made adjustable by including a variable resistance, such as, a resistance 20 in series with the windings l6 and 17.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by letters Patent of the United States, is:

1. In combination. a pair of make and break control contacts, an electromagnetic relay, and a power amplifying arrangement having an input circuit with resistance characteristics connected to said contacts and an output circuit with variable reactance characteristics connected to Ill) said relay, said amplifying arrangement also having a time delay characteristic.

2. In combination, a circuit controller having apair of make and break control contacts, an in--' ductive device under the control oi said contacts, and a saturable core reactor having a direct current control winding connected in series with said contacts and an alternating current windingconnected in series with said inductive device.

3. In combination, a contact-making metenan electromagnetic relay, and a saturabie core rewactor having a direct current control winding in" circuit with the contacts of said meter and an alternating current winding in circuit with said relay.

4. In combination, make and break control contacts, a relay having an inductive winding, a magnetic amplifier having an alternating current winding and a direct current winding; a rectifier, and an alternating current supply circuit, said inductive relay winding and said alternating current amplifier winding being connected in series to said alternating current supply circuit and said contacts, said rectifier and said direct current amplifier winding being connected in series to said alternating current supply circuit.

5. The combination with a saturable core reactor having a direct current control winding and'a pair of parallel connected alternating current windings, of an alternating current supply circuit, a full wave rectifier and a pair of make and break control contacts connected to said direct current winding, and an inductive device connected in series with said supply and said alternating current windings.

I. A control system having in combination. a source of alternating current, an inductive load device, a pair or make and break control contacts, a full wave rectifier having alternating c'urrent'input direct current out putte'rminals, a 'saturable core reactor having a direct current control winding and an alternating having direct current terminals and alternating current terminals, and a saturable core reactor having a direct current control winding connected in series circuit relation with said source and the direct current terminals of said rectifier, said reactor also having a pair of parallel connected alternating current windings connected in series circuit relation with said relay winding and said source, said contacts being connected in series with said source and the alternating current windings of said rectifier. I

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